There is no absolutely reliable early warning system for volcanic eruptions. But before a mountain explodes, it emits warning signals days in advance: Earthquakes occur, volcanic gases rise, the subterranean magma chambers fill up and literally inflate the mountain. When Nyiragongo erupted in the Democratic Republic of Congo on May 22, 2021, the volcanic mountain did not even produce these signs. Now a working group led by Delphine Smittarello from the European Center for Geodynamics and Seismology in Walferdange has found out how the eruption near Lake Kivu came about. The researchers write in the journal “Nature” that a huge layer of magma had formed at a comparatively shallow depth. Therefore, when the volcano erupted, the lava could come to the surface relatively quickly.
The Nyiragongo is located in the Democratic Republic of the Congo, not far from the border with Rwanda. The volcano rises to 3470 meters above sea level, and its cone is filled with a 200 to 250 meter wide, always bubbling lava lake. The city of Goma on the Congolese side and the city of Gisenyi in Rwanda are located near the volcano. Before the strong eruption in 2021, the Nyiragongo already spat in 1977 and 2002. Both times the eruptions were announced a few weeks to days before by strong earthquakes. It was different in May 2021: the monitoring system only reported strong volcanic activity 40 minutes before the eruption. A lava flow then gushed out of the mountainside, devastating a settlement area. Thousands of people fled their homes in panic, hundreds of people were injured and around 220 died.
The research group led by geophysicist Smittarello has now analyzed the measurement data recorded in 2021. Why did the Nyiragongo show the typical warning signals so late? “This very short period of time between the first earthquakes and the eruption on the volcanic flank shows us that the magma took very little time to reach the surface because it was already stored at a shallow depth,” says Smittarello, according to a press release from the European Center for Geodynamics and Seismology. Apparently, a huge magma bubble of 243 million cubic meters had accumulated under the city of Goma. At a depth of only about 500 meters, the magma moved in what is known as a dyke – a shallow layer.